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authorOleg Nesterov <oleg@redhat.com>2010-06-11 20:04:46 +0200
committerIngo Molnar <mingo@elte.hu>2010-06-18 10:46:57 +0200
commit8d1f431cbec115a780cd551ab1b4955c125f8d31 (patch)
treef71e707f0ff495582bd2f43017c87b2ac6ec519d /kernel/posix-cpu-timers.c
parent0bdd2ed4138ec04e09b4f8165981efc99e439f55 (diff)
downloadlinux-8d1f431cbec115a780cd551ab1b4955c125f8d31.tar.bz2
sched: Fix the racy usage of thread_group_cputimer() in fastpath_timer_check()
fastpath_timer_check()->thread_group_cputimer() is racy and unneeded. It is racy because another thread can clear ->running before thread_group_cputimer() takes cputimer->lock. In this case thread_group_cputimer() will set ->running = true again and call thread_group_cputime(). But since we do not hold tasklist or siglock, we can race with fork/exit and copy the wrong results into cputimer->cputime. It is unneeded because if ->running == true we can just use the numbers in cputimer->cputime we already have. Change fastpath_timer_check() to copy cputimer->cputime into the local variable under cputimer->lock. We do not re-check ->running under cputimer->lock, run_posix_cpu_timers() does this check later. Note: we can add more optimizations on top of this change. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <20100611180446.GA13025@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/posix-cpu-timers.c')
-rw-r--r--kernel/posix-cpu-timers.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index d5dbef5e89e6..f66bdd33a6c6 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -1287,7 +1287,10 @@ static inline int fastpath_timer_check(struct task_struct *tsk)
if (sig->cputimer.running) {
struct task_cputime group_sample;
- thread_group_cputimer(tsk, &group_sample);
+ spin_lock(&sig->cputimer.lock);
+ group_sample = sig->cputimer.cputime;
+ spin_unlock(&sig->cputimer.lock);
+
if (task_cputime_expired(&group_sample, &sig->cputime_expires))
return 1;
}